TonyC

iTrader: (1)

Has anyone used this combo? (I'm pretty sure this is the right one, some guy tried to explain it to me, I was watching girls ) The large bore of the 400 block should give it lots of torque (right?). The short 327 stroke should give it the ability to rev higher (right?). And the long rods are good because you typically want the longest rod possible (I read this FAQ about rod theory and that was kind of the main idea of the article). Any comments or insight on this topic would be greatly appreciated. Thanks, Tony

-Don't buy any wooden nickels

QwkTrip

iTrader: (22)

The length of the stroke has a far more profound effect on torque then the bore diameter. The 400 is torquey because of the longer stroke then the 350, not the bore. By installing a short stroke 327 crank you've killed the torque. Now you have to wind the pee water out of the motor to make any power. Rev ability has to do with air management and quality assembly of the motor. You can build a 383 stroker that will rev to 9000 rpm.

AlkyIROC

It would make a good road racing engine.

Nascar engines are designed similar. They don't need low end torque but a high RPM HP. They don't use 400 blocks but the idea is the same. The big bore, short stroke would make little torque but very high rpm HP.

I don't think you could put 6" rods on such a combination. The wrist pin would be up in the compression rings of the piston.

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Follow my racing progress on Stephen's racing page
and check out the race car

87 IROC-Z SuperPro ET Bracket Race Car
461 naturally aspirated Big Block

Best ET on a time slip: 11.242 altitude corrected to 10.89
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87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley

[This message has been edited by Stephen 87 IROC (edited August 07, 2001).]

86 sports coupe

Drag racing engines favor big bore small stroke.Some people say build as much horsepower as possible and gear accordingly.

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83 berlinetta currently 350/350 3:42 gear,2500 stal,3inch exhaust,2 1/4
exhaust manifolds,comp cam 268,performer intake
L69 dual snorkle aircleaner 3160lb

BadSS

Actually the 3.25" stroke with the 6.125" rods is and has been the hot ticket for the roundy round guys that are limited to 358 cubes or less. The big bore allows for big valve and less shrouding effect, the longer rods allow for more dwell at TDC and the piston speed is such (with the short stroke) that you can rev it on up with less worry of the engine coming apart. Plus the 3.25/6.125 combo gives you a high rod to stroke ratio (1.88) and still leaves enough room for 1.25” of compression height,, which does not require the use of oil ring support rails. Cubes are cubes and the power curve from a 4.030/3.48/5.7 combo will be similar to the 4.155/3.25/6.125 when different camshafts are utilized to optimize an RPM band. However, for the reasons stated above,, the over all efficiency of the 4.155/3.25/6.125 would be better. HP per cubic inch,, this is one mean combo when properly prepared - just not practical for the typical build,, and a waste of perfectly good cubic inches, IMO. I’d stroke a 350,, but never destroke a 400,, unless I was running in a restricted or weight limited class,, or turbo-charging the sucker.

QwkTrip

iTrader: (22)

That is absolute 100% bull crap. You're false information could result in this guy building a motor that he absolutely hates. Beef up your knowledge before you make statements like that.

83CrossfireBomb

hot rod magazine built that exact combo

they used a 400 block, 3.25 inch crank, factory forged ford inline 6 rods machined to fit , afr aluminum 305 style heads with small valves, custom forged pistons, RPM manifold and 750 edelbrock right out the box, and a little better than stock 93 Z28 roller cam.

they had over 400 horse and even more torque all the way through the powerband.

the engine had 11:1 compression and ran just as good on 87 oct and it did on 93oct.

they built it for under $3000 too.

ill dig that issue out of storage and find out what issue it was if anyone is interested.



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former 305 crossfire fuel injection
350 cubes
hooker headers
750 vac secondary
700r4 with shift kit

BadSS

Many accomplished drag racers use that philosophy. Large bore short stroke combinations will deliver higher HP per CID,, and if you’re in a displacement limited class,, once you get to a certain point,, the only way you have to increase horsepower is by increasing the rpm band – bigger heads, bigger cam, bigger induction system. When you do so,, you have to gear and run a higher stall speed converter. So there is nothing wrong with 86’s statement “Drag racing engines favor big bore small stroke. Some people say build as much horsepower as possible and gear accordingly.” Even in an unlimited class, where you want to big bore AND big stroke,, you still have to build as much horsepower as possible, which usually means jacking the RPM band up, rev the crap out of it, and gear accordingly!! So 100% bull crap it ain’t – I hear what you’re saying though and agree this philosophy is probably not the best approach to take with a typical street driven engine - but he did say drag racing.

Hot Rod’s build that was referenced was not a good combination of parts to showcase a short stroke build – all in all, a waste of a good 400 block in my opinion. A regular old 350 would have faired just as well (if not better) with the same parts - maybe on 89 octane gas,, 93 for sure.




[This message has been edited by BadSS (edited August 08, 2001).]

Tas

drag racers favor torque. "HP sells cars, but TQ wins races" as the old saying goes.

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-Tas
'89 Formula WS-6

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87RS402

In reality it's only about 90%.

While the fuel classes do like a short stroke to be able to rev easier for a higher top speed using only one gear, those are the people saying to build as much hp and gear accordingly. Other classes, like the one's that are a more street based catagory, like a longer stroke vs. bore. When you have 5000+ hp and the car only weighs 2800lbs what does it matter to us when we're only dealing with 1/10th the power and have to carry 600-800 more lbs? Need examples? Look at motorcycles, the ZX1000 kawisaki uses a short stroke and a very large bore comparitivly. The result more than twice as much hp than torque. It only weighs in at about 450 lbs if that much and will run 10's right off the showroom floor. I produces at least 150 hp, about the same a a base LG4. Now try to pull 3500lbs with it. It doesn't work.

Tas nailed it with his post.

BadSS

Usually when I feel like I've answered the question and it gets off topic I won't continue replying,, but I have to ask 87RS402,, if he thinks I should replace my 614HP SBC engine with "only" 567TQ,, that I shift at 7100rpm with a 600 HP Cummins with over three times the torque that shifts around 1800rpm???? Cause that makes about as much sense as replacing a 150 HP 5000cc 305 with a 150HP 1000cc motorcycle engine.

It's all about making an engine work in its applicable environment - and that requires a balance of "power". For a SBC,, I like 4.155 bores and 3.75 or 3.875 stroke engines myself,, and like I said earlier,,, I'd stroke a 350 before I'd de-stroke a 400,, so I don't think we totally disagree, it's just you can't argue about the shrouding problem a typical SBC head has,, and increasing the bore size is a way to help that situation when large valves are need to make the power level you're looking for,, just leave the 3.75" stroke alone - unless (once again) you're in a limited class category!!

87RS402

That depends on the intended application. If your going to try to pull tens of thousands of pounds around the country, yes.

BadSS

agreed

TonyC

iTrader: (1)

When does the bore:stroke ratio become blown out of proportion? or in other words, when is the bore "too big" for the stroke or when is the stroke "too long" for the bore? This is in terms of useable street hp. Is there an "ideal" bore:stroke ratio and which (small block) engine most closely matches this (while retaining adequate cubic inches)?

QwkTrip: "Rev ability has to do with air
management and quality assembly of the motor. You can build a 383 stroker that will rev to 9000 rpm."

True, but will a 350 rev higher than that 383 provided they have the same build quality?

-Don't buy any wooden nickels

[This message has been edited by TonyC (edited August 09, 2001).]

QwkTrip

iTrader: (22)

That's question is too open ended. A 350 and 383 are the same class of engine. There is no significant design difference that make the conclusion obvious. You're now at a level that's far too complicated to debate. There are many variables that limit rpm potential including reciprocating mass, material strength, rod length, piston design, compression, cam profile, valve spring stiffness and damping, pushrod strength, head design, valve design, exhaust, vehicle weight, vehicle speed, weather, tires, ect... You can only guess at the results at the operating extremes. Which item will break first? Which item is underdesigned? There are so many design variables and effective design alternatives that you simply have to use best judgement and test and test and test.

JoelOl75

A 383 that revs to 9000rpm can never be streetable. It would require the lightest pistons, aluminum rods, $teel crank and dykes rings that seal only under wot.

Piston speed should be kept as low as possible for a motor to live a long life with streetable rings. Quality of build is always a givin (or should be).

Its a better idea to cam a long stroke motor to use its low rpm torque and a short stroke motor for its revs. Kinda lame putting a RV cam in a 302 chevy.

TonyC

iTrader: (1)

QwkTrip:
"There is no significant design difference that makes the conclusion obvious"

What I was trying to get at is will the longer stroke of the 383 affect its ability to rev? Actually that's probably a poor question, lemme' rephrase that, would it cost less to get a 350 to rev. to 7000 than a 383? In other words, is there extra quality that has to be built into the 383 to get it to rev. that high that would be just extra costs in the 350? Like would the 383 need aluminum pistons but the 350 would only need steel?

I understand that a longer stroke creates more torque (like a torque wrench, longer the wrench, the more torque). I'm trying to get at cost/rpm and which would be more cost effective, the short stroke or the long stroke

P.S. your car is amazing, how's the swap coming?

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-Don't buy any wooden nickels

[This message has been edited by TonyC (edited August 10, 2001).]

QwkTrip

iTrader: (22)

I don't have enough experience putting motors together to address the cost issues. Maybe someone else will know.

Thanks for the compliment. The car is coming along fine. I'm just waiting for a slug of parts right. Hopefully I'll fire it up some time in September or October.

83CrossfireBomb

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former 305 crossfire fuel injection
350 cubes
hooker headers
750 vac secondary
700r4 with shift kit

[This message has been edited by 83CrossfireBomb (edited August 10, 2001).]

[This message has been edited by 83CrossfireBomb (edited August 10, 2001).]

BadSS

83CrossfireBomb, coming from memory they used a small runner, small chambered head (unmodified 58cc)using a 2.00 intake valves - is this correct? If so,, where the real benifit comes from the large bore is running big valved heads (2.08+) with the chamber worked accordingly. So,, I'm saying with no bigger valve in the small volume heads,, and no chamber work done,, the longer stroke and shorter rod to stroke ratio of the typical old 350 would have faired as well or better - if I may add in the rpm band tested. I wish I had noted that "typical" 350 builds use the 190 or 195 AFR heads with 2.02 valves and 68cc chambers which I'm sure flow better than the smaller runner volumed, 2.00, 58cc head,, "shrouded" or not. It just was not a favorable build in my opinion to "show case" the real added power a 4.155/3.25 build can give you over a 4.03/3.48 in a racing application. It however was not an article to do that. It met their objectives and goals they set and I'm sure was deemed a success in their mind. However,, I stil think it was a waste of a perfectly good 400 block IMHO.